In creating digital images on photosensitive media there are at least two different imaging applications each with different requirements. The first application is for large format high quality images with fine text and graphics in which the production speed is not critical. These images are up to approximately 12 inches in width and use spot densities over 400 spots per inch. The second application is for smaller format images with large text and a requirement for high production speeds. In these images, the width is about 5 inches or smaller and the spot density is below about 400 spots per inch. In order to minimize the floor space required by two machines, it would be advantageous to use a single scanner in which the format and spot density can be switched easily between the two applications described. In addition, the scanner should use a single paper path for both formats and the cost to manufacture such a scanner should be lower than that of two separate machines.
Printing more than one image resolution with one scanner has been done by using a scanner with a reflecting surface which varies in width in the scanning direction. See G. Starkweather, U.S. Pat. No. 3,944,323. Other methods of using more than one image resolution with one scanner are shown in U.S. Pat. Nos. 5,289,001; 5,274,492; 5,255,115; 5,239,313; 4,953,036; 4,734,715; 4,578,689. None of these patents disclose the use of multiple polygons and none use more than one scan length.
The use of more than one format is described in U.S. Pat. Nos. 4,651,170 and 4,651,169 by J. Chandler, D. Kessler, and E. Muka. In these patents, the format in the line scan direction, the scan length, is changed by adjusting the space between the polygon deflector and the image forming medium. In order to maintain the beam focus on the medium in the scan section of the beam, the optics prior to the polygon deflector are modified. Also, the cylindrical mirror following the polygon is tilted and shifted in order to maintain the polygon mirror facet conjugate with the image forming medium. The page scan format is changed via a speed change in the moving medium. None of these patents, however, disclose a method or apparatus for multiple formats without changing the scan length or changing the attitude of the polygon deflectors.